swarm UI: one request for every agent's linked accounts

GET /api/agents/linked-accounts returns one entry per agent that
/api/agents/status has a row for, as {hive, agent, accounts}, from one
store login. The agents page fetches it once (and again when a link dialog
closes) and hands each table row and the detail panel its agent's slice,
so the page makes no per-agent request. The per-agent route had no caller
left and is removed. The bao grant is unchanged: the same list on each
agent's matrix and forge metadata directories.

Refs #4855

frontend/packages/swarm-ui/src/pages/agents/LinkedAccounts.tsx

@@ -1,13 +1,10 @@
 // <LinkedAccounts> — the accounts linked to one agent, one row each: kind,
-// name, host. Reads `GET /api/hives/{hive}/agents/{agent}/linked-accounts`,
-// which carries names and hosts only, never a credential.
+// name, host. Renders its slice of `GET /api/agents/linked-accounts`, which
+// `AgentsPage` fetches once for every agent (`useLinkedAccounts`) and which
+// carries names and hosts only, never a credential.
 //
-// Fetched on mount and again whenever `version` changes; `AgentsPage` bumps
-// it when a link dialog closes, so an account linked there shows up without
-// waiting for a reload.
-//
-// Its state belongs to one agent: callers key it by hive and agent, so
-// switching agents remounts it instead of showing the previous agent's rows.
+// Callers key it by hive and agent, so switching agents remounts it instead
+// of reusing the previous agent's element.
 import { useEffect, useState } from "preact/hooks";
 import { readApiError, type ProblemDetails } from "@hive/shared/api-error.js";
 import { Badge } from "@hive/shared/badge.js";
@@ -16,60 +13,83 @@ import "./LinkedAccounts.css";
 export type AccountKind = "matrix" | "forgejo" | "github";
 
 // Mirrors `linked_accounts::LinkedAccount`.
-interface LinkedAccount {
+export interface LinkedAccount {
   kind: AccountKind;
   name: string;
   host: string | null;
   reserved: boolean;
 }
 
-export function LinkedAccounts({
-  hive,
-  agent,
-  version,
-  kinds,
-}: {
-  hive: string;
+// Mirrors `linked_accounts::AgentLinkedAccounts`.
+interface AgentLinkedAccounts {
+  hive: string | null;
   agent: string;
-  version: number;
-  /** Only these kinds; all of them when omitted. */
-  kinds?: AccountKind[];
-}) {
-  const [accounts, setAccounts] = useState<LinkedAccount[] | null>(null);
-  const [error, setError] = useState<ProblemDetails | null>(null);
+  accounts: LinkedAccount[];
+}
 
+// What the page holds: each agent's accounts by agent name (the roster's
+// row key), or the error the one fetch failed with.
+export type LinkedAccountsState =
+  | { status: "loading" }
+  | { status: "loaded"; byAgent: ReadonlyMap<string, LinkedAccount[]> }
+  | { status: "error"; problem: ProblemDetails };
+
+// The one fetch, re-run whenever `version` changes; `AgentsPage` bumps it
+// when a link dialog closes, so an account linked there shows up without a
+// reload. Keeps the previous result on screen while a refetch is in flight.
+export function useLinkedAccounts(version: number): LinkedAccountsState {
+  const [state, setState] = useState<LinkedAccountsState>({
+    status: "loading",
+  });
   useEffect(() => {
     let cancelled = false;
     (async () => {
-      const r = await fetch(
-        `/api/hives/${encodeURIComponent(hive)}/agents/${encodeURIComponent(agent)}/linked-accounts`,
-      );
+      const r = await fetch("/api/agents/linked-accounts");
       if (!r.ok) {
-        if (!cancelled) setError(await readApiError(r));
+        const problem = await readApiError(r);
+        if (!cancelled) setState({ status: "error", problem });
         return;
       }
-      const data = (await r.json()) as LinkedAccount[];
+      const data = (await r.json()) as AgentLinkedAccounts[];
       if (cancelled) return;
-      setAccounts(data);
-      setError(null);
+      setState({
+        status: "loaded",
+        byAgent: new Map(data.map((e) => [e.agent, e.accounts])),
+      });
     })().catch((e: unknown) => {
-      if (!cancelled) setError({ detail: String(e) });
+      if (!cancelled)
+        setState({ status: "error", problem: { detail: String(e) } });
     });
     return () => {
       cancelled = true;
     };
-  }, [hive, agent, version]);
+  }, [version]);
+  return state;
+}
 
-  if (error) {
+export function LinkedAccounts({
+  state,
+  agent,
+  kinds,
+}: {
+  state: LinkedAccountsState;
+  agent: string;
+  /** Only these kinds; all of them when omitted. */
+  kinds?: AccountKind[];
+}) {
+  if (state.status === "error") {
     return (
       <Badge
         tone="negative"
         value="accounts unavailable"
-        title={error.detail ?? "listing linked accounts failed"}
+        title={state.problem.detail ?? "listing linked accounts failed"}
       />
     );
   }
-  if (accounts === null) return <span class="ui-linked-accounts-muted">…</span>;
+  if (state.status === "loading") {
+    return <span class="ui-linked-accounts-muted">…</span>;
+  }
+  const accounts = state.byAgent.get(agent) ?? [];
   const shown = kinds
     ? accounts.filter((a) => kinds.includes(a.kind))
     : accounts;